In cooling towers, water, for example from a secondary condensation circuit, is mainly cooled by vaporizing a fraction of the water to be cooled which trickles over surfaces which are provided for this purpose and over which a stream of air flows in the opposite direction to the trickling direction, and secondly during the convection which takes place on the heat exchange surfaces in the water itself.
These surfaces are carried by a heat exchange body, commonly called “packing”, formed by sheets which are usually made from PVC but are sometimes metal, assembled together to form a cellular structure. Each cell of this structure takes the form of a tube approximately 1.5 meters long, the average dimension of its cross section being a few centimeters. The wall of the cells is thin (a few tenths of a millimeter) and may be pierced with a large number of orifices. The heat exchange bodies are suspended in the cooling tower between a unit for spraying the water to be cooled and a lower trough for collecting the cooled water.
Catching means are arranged in the upper part of the tower for retaining, as much as possible, the droplets of water carried by the cooling air. Indeed, it is important not to emit this water into the atmosphere as it contains germs which may have proliferated in the tower where the temperature favors such proliferation.
During use, the heat exchange body becomes loaded with a deposit of mineral salts (scale) because of the evaporation that occurs on the trickling surfaces. This deposit increases over time and may represent as much as ten times the weight of the body itself in some installations.
There are many disadvantages of this deposit: it obstructs the trickling and hence affects the efficiency of the heat exchange; various germs in the water can collect there in an environment that is favorable to their proliferation; it applies a very significant extra load on the support structure for the heat exchange body which is generally suspended inside the tower, etc.
There are, at least in theory, many means of overcoming this disadvantage.
One of these consists in chemically treating the water to be cooled to remove salts from it and hence prevent the heat exchange surfaces from scaling up. This method cannot be considered for cooling towers of electricity-generating, thermal, or nuclear power stations.
The scale can also be dissolved chemically using suitable solutions. This approach entails the awkward problem of treating the effluents, which has economic consequences for the cost of the operation.
It may be envisaged to shake the heat exchange body using any suitable mechanical means; although this method has been tested, it damages the heat exchange body, making it virtually unusable subsequently.
Lastly, this heat exchange body may be mechanically cleaned after it has been disassembled; this is an extremely expensive operation given the large size of this body (10 to 12,000 cubic meters in units of approximately two cubic meters).
FR 2.903.178 discloses a method and a machine which makes it possible to avoid the disadvantages of the existing or foreseeable solutions in order to clean the heat exchange bodies employed in air-cooling towers of electricity-generating power stations, in particular nuclear power stations.